Geographic Range

Diadema antillarum is found in the shallow waters of the Atlantic Ocean, in the Bahamas, and the Western Atlantic from eastern Florida to Brazil. In the Eastern Atlantic D. antillarum is found in Madeira, the Gulf of Guinea, and the Canary, Cape Verde, and Annabon islands. (Hendler, et al., 1995)

Physical Description

Diadema antillarum is a regular (round) urchin, and displays the pentamerism of echinoderms. Mature individuals of D. antillarum can reach up to 500 mm in diameter. Diadema antillarum has thin spines that range from 300-400 mm in length and can be up to four times the diameter of the test (skeleton formed inside the body). The spines are thin, hollow, and break easily. The test is rigid and there is a reduced amount of soft tissue in the body wall as compared to other species in the family Diadematidae.

The test and spines of a mature adult are typically black, but lighter colored spines may be intermixed, and in rare cases the urchin will be almost entirely white. The spines of juveniles are always banded with black and white. When the urchin dies, the spines falls off and the test remains.

Development

The fertilized egg has two forms: the blastula and the gastrula. These swim close to the surface of the water with the aid of cilia, and can be dispersed quite far, depending on currents. These larvae are known as the echinopluteus, and can remain in the larval stage for an average of 4-6 weeks. As the larvae mature, a vestibule is created in what will be the oral side of the urchin. Tentacles grow from this opening, on which suction areas eventually emerge. When the tentacles have suckers, they are primary poda, which serve as locomotive tools when the larva sinks to the ocean floor. At this point the skeletal plates begin to develop. When the 5 ambulical plates are developed and the terminal plate lies next to the genital plates, the urchin is fully developed, though it will continue to grow for the rest of its life. (Grzimek, 1972)

Reproduction

Some populations of D. antillarum have been observed to congregate during their spawning season. There is no mating of individuals as fertilization and gestation occur in the open water. (Grzimek, 1972)

The spawning of D. antillarum appears to be connected to the lunar calendar. During the summer season, the egg and sperm are released once during each lunar month. This spawning period is dependant upon temperature; populations in different hemispheres may spawn at different times depending on when the warm season occurs.

The egg and sperm are released into the water where they are fertilized and develop into the larval echinopluteus. Egg size has also been observed to change during the month. Spawning occurs when the eggs are largest. (Anonymous, 1967; Grzimek, 1972; Hendler, et al., 1995)

Lifespan/Longevity

The lifespan of D. antillarum is closely related to temperatures and food availability. Populations in warmer climates tend to have a quicker rate of development and shorter lifespan than those in colder climates. (Grzimek, 1972)

Average lifespanStatus: wild

6 years

Typical lifespanStatus: wild

4 to 8 years

Behavior

Extremely sensitive to light, D. antillarum remains in darker areas, like crevices in the reef, during the day, and emerges at night to feed. Groups of individuals can be found in open areas, and densities can reach up to 20 per square meter. This group size corresponds to the abundance of predators in the area.

A very active urchin, D. antillarum has a high reactivity and sensitivity to changes in light and water disturbances. The urchin will wave its spines in the direction of the upsetting occurence, and retreat to sheltered areas quickly, if need be. (Banister and Campbell, 1985; Hendler, et al., 1995)

Communication and Perception

Diadema antillarum has a highly developed light sensitivity. When a shadow appears, the urchin waves its spines in the direction of the shadow and moves away from the shadow, often into a more protected area. In this sense, D. antillarum can almost 'see' predators. It is not known how individuals communicate with each other to aggregate. (Waller, 1996)

Predation

The spines of Diadema antillarum are brittle and will fragmentize if wounded. The pieces are difficult to remove, and often cause infections as they carry bacteria. The mucous coating of the spines, normally used to kill organisms that live in the spines, carries a mild poison that also aids in deterring smaller predators. Diadema antillarum has been observed to gather in groups as an added protection. (Carson, 1955; Grzimek, 1972; Hendler, et al., 1995; Waller, 1996)

Ecosystem Roles

Diadema antillarum feeds on the algal turf of the coral reefs. The algal turf grows rapidly, and without the urchin's control, can destroy the reefs. Diadema antillarum clears the reefs, making room for coral larvae to settle and grow. However, the urchin actually wears away at the calcium carbonate of the reef, too. (Hendler, et al., 1995)

Economic Importance for Humans: Negative

The spines of D. antillarum are very sharp and can easily pierce skin, shoes, and wetsuits. Contact with a spine is not extremely painful, but the shattering of the spine leaves organic material in the wound that can cause intensely painful infections. The poisonous mucous seems to have very little effect on humans. (Carson, 1955; Hendler, et al., 1995)

Negative Impacts

injures humans

bites or stings

Conservation Status

Other Comments

In 1983 D. antillarum experienced a massive die-off all across the Caribbean; some areas lost up to 97% of mature individuals. The die-off is thought to be due to a water-borne pathogen that has not yet been identified. The great reduction of D. antillarum in the reefs caused an extreme increase in the algal cover, and thus a reduction of larval coral settlement. Microalgae has become more abundant in the time since the die-off; the greater amount of algae allows the reefs to support a greater number of herbivorous fish, which can result in more damage to the reefs. (Bruckner and Bruckner, 1998; Hendler, et al., 1995)

Contributors

Glossary

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

photic/bioluminescent

generates and uses light to communicate

radial symmetry

a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Anonymous, 1967. The Larousse Encyclopedia of Animal Life. Verona, Italy: McGraw-Hill Book Company.

Banister, K., A. Campbell. 1985. The Encyclopedia of Aquatic Life. New York: Facts of File Publishing.

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.